Dimitrios and I don't think there is a fundamental difficulty here, but it involves some work on the constraint solver that we have not yet done, especially concerning the evidence that is constructed for a proof.
So it's on the list, but currently not very high priority. Yell if it's important to you.
There is a ticket about it: http://hackage.haskell.org/trac/ghc/ticket/4310, so add yourself to the cc list if you care about it.
Simon
| -----Original Message-----
| From: Stefan Holdermans [mailto:stefan at vectorfabrics.com]
| Sent: 21 June 2011 10:51
| To: Simon Peyton-Jones; Tom Schrijvers
| Cc: glasgow-haskell-users at haskell.org| Subject: Type function under a forall type
|| Simon, Tom,
|| I hit this type-error message in GHC 7.0.3:
|| Cannot deal with a type function under a forall type:
| forall e. El e u
|| Is there a fundamental reason why type functions under a forall type are a bad idea?
| Of is it just something that hasn't been implemented/thought about yet?
|| Cheers,
|| Stefan